Action Potentials

1. What is the difference between the endoneurium, perineurium, and epineurium?
2. What are leak channels?
3. How is the negative potential maintained inside the neuron? What is this normal resting membrane potential?
4. What is an action potential and how is it formed?
5. What does it mean to have an all-or-none response?


Answers:
1. The endoneurium surrounds the individual axon and its myelin sheath. The perineurium is the strong covering that surrounds bundles of nerve fibers. The epineurium surrounds the entire nerve and holds the fascicles together.
2. Leak channels are openings that allow Na and K to move in and out of the neuron membrane.
3. The negative potential is maintained via Na-K ATP-dependent pumps that export three ions of Na and import two ions of K. The normal restinging membrane potential is -70 to -90 mV.
4. The action potential is a voltage change occuring from an excited cell. It results when the cell membrane becomes increasingly permeable to Na, which rushes into the cell through open voltage-gated channels.
5. A stimulus must be strong enough to reach a threshold of activation. If below threshold, no activation will occur. A high enough stimulus will produce an action potential, but higher stimuli will not produce a larger potential.